Never tried Ubuntu, but have heard it's easy to install and has decent hardware detection. Another benefit is its "one package for one task" philosophy - on other linux distros there might be anywhere from 3 to 50 different packages to do the same task (eg DVD burning, or whatever) - at least that's what I've been told...

A recent review in Linux Format rated Fedora 7 very highly. That's what I'm currently using. It's a great little distro actually. Almost everything worked out of the box, and I have some pretty recent hardware. The only exception was my wireless card - had to do a bit of tweaking there. I've had absolutely no stability issues with Fedora 7 (or FC5 for that matter).

With any of the linux distros you can resize and keep your windows partition and make a dual-booting machine (you select the OS you want at boot time from the bootloader). That is also what I've done, as I need some windows-based software for work purposes. It's a good compromise as well if you want to try linux without completely committing. Another option is to get hold of live CDs - you can see what flavour of linux might best suit you without the need to install to your hard disk first.

James.